Once Mamata Banerjee's Man Friday, Mukul Roy's departure has set off rumours of him joining the BJP.

Within hours of senior Trinamool Congress functionary Mukul Roy announcing his decision to step down from the party's working committee and the party after Durga Puja, the party shot back announcing Roy's suspension from the party for six years for anti-party activities.

"We are concerned about our own party. Roy has been unfaithful to the party and our leader. Mamata Banerjee gave him everything — he became railway minister, he was the member of Rajya Sabha — what else do you want? Mamata put a lot of a trust in Roy and he betrayed the party and our leader," TMC secretary general Partha Chatterjee said at a press conference in Kolkata.

“We have heard that Mukul Roy has decided to quit Trinamool Congress after Durga puja. For last few years he has been indulging in anti-party activities and tried to weaken the party. The disciplinary committee of Trinamool Congress has recommended punishment against Mukul Roy to party chairperson Mamata Banerjee and Roy has been suspended from the party for six years,” Chatterjee said.

Earlier today, Roy, once the undisputed number two who had served as the Union Railways minister under the erstwhile UPA government, quit the party’s working committee and announced that he will resign from the party as well as his Rajya Sabha seat after Durga Puja.

“I was the one who was the first to sign, when Trinamool Congress was formed in December 17, 1997. With a heavy heart today, I have decided to separate myself from the party. I will reveal the reasons after the Durga Pujas,” Roy said addressing journalists at a press conference called in the state capital Kolkata today.

Roy said he has communicated to the leadership his decision to step down from the party working committee. He will be resigning from his Rajya Sabha seat as well as the primary membership of the party.

“I shall resign from Rajya Sabha immediately after the pujas. About eight months are left for my tenure to end in the Upper House. At the same time, I will also leave the primary membership of the party,” Roy said.

Roy’s departure has set off speculation of his joining the Bharatiya Janata Party (BJP) which is fast emerging as the TMC’s main challenger in the state. There is also talk of Roy forming an independent party on his own.

The exit comes after reports of a growing rift between Roy and Mamata Banerjee, especially around the Assembly elections in the state. Sidelined in the party, Roy and his followers had a fallout with the party but were reinstated later.

However, Roy was removed from various posts of the party recently.

On September 20, Roy asked that the Z category security he was entitled to be stopped. On Sunday, he went to the inauguration of a Durga Puja that is identified with Rajya Sabha MP Kunal Ghosh, who was suspended by the party after he spoke out against the chief minister in the Saradha scam.

Mukul Roy, 63, was once the undisputed number two in the party after Mamata Banerjee. His utility stemmed from the fact that he was responsible for expanding and managing the organisation both in Bengal and beyond it. He was also instrumental in party strategy during the polls, especially in the 2014 Lok Sabha elections.

Also Mamata’s troubleshooter, Roy replaced Mamata as Railways minister when the latter stepped down from UPA I government to contest the Assembly elections from Bhawanipore constituency. He was the railway minister from March 20, 2012 to September 21, 2012.

Roy’s son, Subhrangshu, is also a TMC MLA from Bijpur constituency from North 24 Parganas district. He first won in 2011 and was reelected in 2016.